linux-kernel - Re: [PATCH] relay: use kvcalloc to alloc page array in relay_alloc_page

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Date:   Fri, 9 Sep 2022 14:48:13 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     wuchi <wuchi.zero@...il.com>
Cc:     hch@....de, axboe@...nel.dk, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] relay: use kvcalloc to alloc page array in
 relay_alloc_page_array

On Fri,  9 Sep 2022 18:10:25 +0800 wuchi <wuchi.zero@...il.com> wrote:

> The kvcalloc is safer because it will check the integer overflows,
> and using it will simple the logic of allocation size.
> 
> ...
>
> --- a/kernel/relay.c
> +++ b/kernel/relay.c
> @@ -60,10 +60,7 @@ static const struct vm_operations_struct relay_file_mmap_ops = {
>   */
>  static struct page **relay_alloc_page_array(unsigned int n_pages)
>  {
> -	const size_t pa_size = n_pages * sizeof(struct page *);
> -	if (pa_size > PAGE_SIZE)
> -		return vzalloc(pa_size);
> -	return kzalloc(pa_size, GFP_KERNEL);
> +	return kvcalloc(n_pages, sizeof(struct page *), GFP_KERNEL);
>  }

It isn't really equivalent because kvcalloc() may attempt a large
kmalloc() request, whereas the current relay_alloc_page_array()
implementation avoids this by choosing vmalloc() instead.

But I doubt if it matters - kvcalloc()->kvmalloc_node() does take some
care to prevent that large kmalloc() request from being too disruptive.